1. Field of the invention
The present invention relates to high-reliability computer systems comprising a plurality of computers with a redundancy arrangement on a voting basis.
2. Description of the Prior Art
Prior art high-reliability computer systems of the type referred to above are often used in such application that demand a high operational reliability, since, in the voting system, a failure in constituent elements of the computer system leads to no immediate failure of the overall computer system and the computer system operation is not interrupted by redundancy switching operation, software retry and the like.
Recently, an increased importance of the role of computers in rockets, space vehicles and the like demands the flight and/or interior control of such vehicles to be fully computerized. Accordingly, more and more large and ultra-large scale integrated circuits (LSI and ultra-LSI) with increased circuit integration or density are used rather than the conventional small and medium scale integrated circuits (SSI and MSI). The current technological study is directed to achieve higher function/performance and smaller dimensions/lower power consumption at the same time.
On the other hand, an LSI microprocessor has had a problem of such a so-called single event phenomenon that the LSI, when subjected to high energy of cosmic rays traveling in the cosmic space, loses information stored therein, thus disabling the operation of the LSI. Such single event phenomenon is said to take place once or so in a time period of from several hours to several months in probability, and varies depending on the strength of the LSI, frequency of actuation, etc.
Further, since computers have become the nucleus of space vehicles or the like, the failure or inoperability of the computer has become umpermissible or intolerable even if only momentary. In addition, it is impossible to repair such a faulty computer mounted on a space vehicle far away from the earth, and hence there has been studied such a high-reliability computer system that uses three or more computers on a voting basis.
However, this voting system, though having the aforementioned merits, has been disadvantageous in such applications that require a very high reliability as mentioned above, because the system also has the following disadvantages.
1. Failure of a voter leads to failure of the overall computer system.
2. When a voter with redundancy arrangement is used, it becomes necessary to switch over the faulty portion in case of a failure, which requires re-runining the software, usually causing the processing to become discontinuous.